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PHYSICAL BIOSCIENCES DIVISION ONE STOP

Heinz Frei


Chemist Senior Scientist
Former Division Deputy Director, Leader
Interface Project, Joint Center for Artificial Photosynthesis

Natural & Artificial Photosynthesis

Contact info:


Lawrence Berkeley National Laboratory
One Cyclotron Road
Building 66
Berkeley, CA 94720 USA

Bldg. 66, Rm 308


Primary Phone: 510-486-4325
E-mail: HMFrei@lbl.gov


Research Emphasis:

Recent Publications:

N. Sivasankar, W.W. Weare, and H. Frei.  Direct Observation of a Hydroperoxide Surface Intermediate upon Visible Light Sensitized Water Oxidation at Ir Oxide Nanocluster Catalyst by Rapid-Scan FT-IR Spectroscopy. J. Am. Chem. Soc. 133, 12976-12979(2011).

H.S. Soo, M.L. Macnaughtan, W.W. Weare, J. Yano, and H. Frei.  EXAFS Spectroscopic Analysis of Heterobinuclear TiOMn Charge-Transfer Chromophore in Mesoporous Silica.  J. Phys. Chem. C, submitted.

N. Sivasankar and H. Frei.  Direct Observation of Kinetically Competent Surface Intermediates upon Ethylene Hydroformylation over Rh/Al2O3 under Reaction Conditions by Time-Resolved FT-IR Spectroscopy. J. Phys. Chem. C 115, 7545-7553 (2011).

T. Cuk, W.W. Weare, and H. Frei.  Unusually Long Lifetime of Excited Charge-Transfer State of Binuclear TiOMnII Unit Anchored on Silica Nanopore Surface. J. Phys. Chem. C 114, 9167-9172 (2010).

F. Jiao and H. Frei.  Nanostructured Manganese Oxide Clusters Supported on Mesoporous Silica as Efficient Oxygen-Evolving Catalysts. Chem. Commun. 46, 2920-2922 (2010).

F. Jiao and H. Frei. Nanostructured Cobalt and Manganese Oxide Clusters as Efficient Water Oxidation Catalysts. Energy Environ. Sci. 3, 1018-1027 (2010).

H. Frei.  Polynuclear Photocatalysts in Nanoporous Silica for Artificial Photosynthesis. Chimia 63, 721-730 (2009).

F. Jiao and H. Frei.  Nanostructured Cobalt Oxide Clusters in Mesoporous Silica as Efficient Oxygen-Evolving Catalysts. Angew. Chem. Int. Ed.48, 1841-1844 (2009).

X. Wu, W.W. Weare, and H. Frei.  Binuclear TiOMn Charge-Transfer Chromophore in Mesoporous Silica. Dalton Trans., 10114-10121 (2009) (Hot Article).

W. Weare and H. Frei.  Artificial Photosynthesis, In: Yearbook of Science and Technology; Weil, J., Ed.; McGraw Hill: New York (2009); pp.28-31.



Summary:

The goal of our research is to develop robust artificial photosynthetic systems for the synthesis of fuels and chemicals from carbon dioxide and water using sunlight as energy source. To take advantage of the flexibility and precision by which light absorption, charge transport and catalytic properties can be controlled by discrete molecular structures, we are assembling well-defined inorganic polynuclear units in nanoporous silica scaffolds that function as visible light photocatalysts for carbon dioxide reduction or water oxidation. Photocatalytic units anchored on silica nanopore surfaces consist of an oxo-bridged binuclear metal-to-metal charge-transfer chromophore that acts as a visible light electron pump coupled to a multi-electron transfer catalyst (Figure). Selective synthetic methods are being developed that afford all-inorganic units with donor and acceptor metal centers with selectable redox potential, thus offering a means to achieve desirable light absorption properties and thermodynamic efficiency. The large surface area of the nanoporous silica supports affords the high density of photocatalytic sites needed for the chemistry to keep up with the solar flux, while the nanostructured features offer opportunities for separating the reduction from the oxidation half reaction in an integrated photosynthetic system. Photocatalysts for the efficient oxidation of water to O2 by visible light and for carbon dioxide splitting to CO have been demonstrated.

Emphasis in our work is on the structural elucidation of the photocatalytic units by EXAFS, XANES, FT-Raman, FT-IR, EPR and optical spectroscopy. High resolution transmission electron microscopy and diffraction measurements reveal the structure of metal oxide nanoclusters that serve as multi-electron catalyst inside the silica mesopores. Electron transfer processes of the photocatalytic units are studied by transient optical absorption spectroscopy,while the mechanisms of the water and carbon dioxide activation steps are explored by time-resolved FT-IR spectroscopy on the nanosecond to millisecond time scale. We have been able to detect transient surface intermediate at the gas-nanopore and liquid-nanopore interface using transmission or attenuated total reflection methods. The mechanistic understanding, combined with knowledge of electronic and structural details of the polynuclear photocatalysts are a key ingredient for improving the design of the systems.



Publications